Method for transmitting and receiving signalling information

ABSTRACT

A method for protecting signalling information in a frame to be transmitted to a receiver in a communication system, comprising: encoding frame signalling information of the frame to protect the frame signalling information; and encoding Forward Error Correaction FEC block signalling information of FEC blocks in the frame by using Reed-Muller codes to protect the FEC block signaling information.

FIELD OF THE INVENTION

The present invention relates in general to communication systems, andmore particularly, to a method and apparatus for transmitting andreceiving signalling data in a communication system.

BACKGROUND OF THE INVENTION

Signalling information transportation is very important to acommunication system. If some of the signaling information is lost, itwill have great impact on payload data demodulation. If the channelenvironment is noisy, the proper protection of signalling information isnecessary. For example, DVB-T (Digital Video Broadcast-Terrestrial),DTMB (Digital Terrestrial Multimedia Broadcast, Chinese Terrestrialstandard) and the latest DVB-T2 standard all define signalingprotection.

Digital Video Broadcasting-Cable (DVB-C) is a first generation cabletransmission system (e.g., see EN 300 429 V.1.2.1 (1998-04) DigitalVideo Broadcasting (DVB); Framing structure, channel coding andmodulation for cable systems). However, migration to a second generationcable system, DVB-C2, is currently being studied for protecting thesignalling information.

FIG. 1 is a schematic diagram showing a L1 (layer1) signaling structureused in a DVB-T2 OFDM frame. As shown in FIG. 1, the signalinginformation is split into three main sections: P1 signalling, L1pre-signalling and L1 post-signalling. The P1 signalling is carried byP1 symbols, and used to indicate the transmission type and basictransmission parameters. The remaining signalling is carried out by P2symbols, comprising L1 pre-signalling and L1 post-signalling. The L1pre-signalling enables the reception and decoding of the L1post-signalling, which in turn conveys parameters needed by the receiverto the access physical layer pipes. The L1 post-signalling is furthersplit into two main parts: configurable and dynamic, and these may befollowed by an optional extension field. The L1 post-signalling finisheswith a CRC and padding (if necessary).

In order to protect the L1 signalling information of the OFDM frame inDVB-T2, a concatenation channel code was proposed for performing FEC(Forward Error Correction) encoding for the signaling information, withthe inner code using punctured S2-LDPC codes and the outer code usingshortened BCH codes. This protection scheme can reuse the codex used forthe following data payload of the OFDM frame. From the above-mentioneddescription, it can be seen that signaling information is protected atthe OFDM frame level in DVB-T2. In addition, for DTMB and DVB-T,signaling information is also protected at the OFDM frame level.

SUMMARY OF THE INVENTION

The invention concerns A method for protecting signalling information ina frame to be transmitted to a receiver in a communication system,comprising: encoding frame signalling information of the frame toprotect the frame signalling information; and encoding Forward ErrorCorrection FEC block signalling information of FEC blocks in the frameby using Reed-Muller codes to protect the FEC block signalinginformation.

The Reed Muller codes is selected to encode FEC block signallinginformation, so that the FEC block header can be detected easily in thereceiver, because the symmetry structure of RM codewords can help todistinguish this RM codewords from the data stream by usingautocorrelation calculation.

The invention also concerns a transmitter for implementing the abovemethod for protecting signalling information in a frame. The transmittercomprises a signalling generator for providing respective signallinginformation for each FEC data block of a frame; a FEC encoder forencoding the respective signalling information; and a frame builder forforming an encoded FEC block including encoded signalling informationand a corresponding FEC data block.

According to an embodiment, the signalling information generator of thetransmitter further provides signalling information for the frame; theFEC encoder further encodes the frame signalling information and theframe builder further form an encoded frame including the encoded framesignalling information and the encoded FEC block.

The invention also concerns a method for receiving signallinginformation in a frame from a transmitter in a communication system,comprising: receiving a encoded frame signalling information and encodedFEC block signalling information of the frame; and decoding the encodedsignalling information so that a corresponding FEC data block isrecovered, wherein the encoded FEC block signalling information is aReed-Muller codes encoded FEC block signalling information.

The invention also concerns a receiver for implementing the above methodfor decoding an encoded frame. The receiver comprises a means forreceiving respective encoded FEC block of the frame, including a FECdata block and encoded signalling information for the FEC data block;and a FEC decoder for decoding the respective encoded signallinginformation so that a corresponding FEC data block is recovered.

According to an embodiment, the means for receiving of the receiverfurther receives an encoded frame including an encoded frame signallinginformation, and the FEC decoder further decodes the encoded framesignalling information so that the frame is recovered.

BRIEF DESCRIPTION OF DRAWINGS

These and other aspects, features and advantages of the presentinvention will become apparent from the following description inconnection with the accompanying drawings:

FIG. 1 is a schematic diagram showing a L1 signaling structure used in aDVB-T2 OFDM frame;

FIG. 2 is an illustrative block diagram showing a communication systemcomprising a transmitter and a receiver according to an embodiment ofthe invention;

FIG. 3 is a block diagram of RM encoding for FEC signalling according tothe embodiment of the invention;

FIG. 4 is a schematic diagram showing a encoding scheme for atransmission frame according to the embodiment of the invention; and

FIG. 5 is a schematic diagram showing another FEC encoding schemeaccording to another embodiment of the invention.

DETAIL DESCRIPTION OF PREFERRED EMBODIMENTS

A description will now be given with reference to the attached figuresto illustrate many advantages/features of the present invention,according to various illustrative embodiments of the present invention.

For more information about Digital Video Broadcasting-Terrestrial(DVB-T), see ETSI EN 300 744 V1.4.1 (2001-01); Framing structure,channel coding and modulation for digital terrestrial television; formore information on Digital Video Broadcasting-Cable (DVB-C), see EN 300429 V.1.2.1 (1998-04) Digital Video Broadcasting (DVB); Framingstructure, channel coding and modulation for cable systems); for moreinformation on Digital Video Broadcast-satellite (DVB-S2) system, seeEuropean Telecommunications Standards Institute (ETSI) Draft EN 302307,v.1.1.1, June 2004); for more information on the Chinese DigitalTelevision System, see (GB) 20600-2006 (Digital MultimediaBroadcasting—Terrestrial/Handheld (DMB-T/H)). For more information on(MPEG)-2 Systems Standard (ISO/IEC 13818-1)). It should also be notedthat the inventive concept may be implemented using conventionalprogramming techniques, which, as such, will not be described herein. Inthis regard, the embodiments described herein may be implemented in theanalogue or digital domains.

It is known that an OFDM frame includes multiple FEC (Forward errorcorrection) data blocks for data symbols such as audio and/or video datato be transmitted. As noted earlier, the signalling structure in DVB-T2is based at the frame level. Thus, all FEC blocks of the data symbols inone T2 frame must obey the same signalling parameters, such as code rateand modulation.

According to an embodiment of the invention, the signalling informationof the FEC blocks is protected by FEC encoding, so it can support VCM(Variable coding and modulation). In that case the signaling informationcan change at the FEC level instead of the frame level.

Referring now to FIG. 2, an illustrative block diagram of acommunication system according to the embodiment is shown comprising atransmitter 100 and a receiver 200. Only those portions relevant to theexplanation of the embodiment of the invention are shown in transmitter100 and receiver 200. In the communication system, the transmitter 100transmits (or broadcasts) an OFDM signal with video and/or audioinformation and FEC encoded signaling information of the OFDM frame tothe receiver 200 through a communication channel, as shown in FIG. 2.

Transmitter 100 comprises L1 signalling generator 102, FEC encoder 104,mapping device 106 and frame builder 108. Alternatively, transmitter 100is a processor-based system and includes one or more processors andassociated memory. In this context, computer programs, or software, arestored in the memory for execution by the processor, e.g., to implementFEC encoder 104. The processor is representative of one or morestored-program control processors and these do not have to be dedicatedto the signalling information protection function, e.g., the processormay also control other functions of transmitter 100. The memory isrepresentative of any storage device, e.g., random-access memory (RAM),read-only memory (ROM), etc.; may be internal and/or external totransmitter 100; and is volatile and/or non-volatile as necessary.

In transmitter 100, L1 signalling generator 102 is adapted to provide L1signalling parameters, e.g., FFT size, the selected guard interval pilotpattern, coding rate and modulation scheme, for each transmitted frameto the receiver 200 according to the DVB transmission standard. Thesignalling parameters can change from frame to frame. How the signallingparameters are selected is irrelevant to the present embodiment andperformed in accordance with the DVB standard. According to theembodiment, the L1 signalling generator 102 also provides signallingparameters such as code rate and modulation, for each FEC block of datasymbols in the frame. The signalling parameters can also change from FECblock to FEC block, that is, Variable coding and modulation (VCM) isimplemented.

FEC encoder 104 is adapted to encode the signalling parameters for eachframe so as to form an encoded frame by frame builder 108 which will bedescribed later, e.g., the frame is encoded by using concatenation codesto protect OFDM frame signaling. In addition, FEC encoder 104 is adaptedto encode the respective signaling parameters for each FEC data block,e.g., by using Reed-Muller codes to protect the FEC signaling so as toform an encoded FEC block by frame builder 108, and the encoded FECblock includes the encoded signalling information and the correspondingFEC data block.

Referring now to FIG. 3, a block diagram of the encoding scheme for FECsignaling by RM codes according to the present embodiment is shown. TheRM codes used to encode the FEC signaling information can be first-orderRM codes(32,6),(64,7), second-order RM codes(32,16),(64,22), sub-code ofthe second-order RM codes(32,10), or shortened RM codes (30,14). Thefinal option depends on the FEC block signaling information bits numberand the channel environment. In the embodiment as shown in FIG. 3, an RMcode (32, 16) is used since the FEC block signalling information bitsnumber is 16. A QPSK mapping process is performed on the encodedsignalling data, so as to get an encoded FEC block.

Returning now to FIG. 2, transmitter 100 modulates the FEC encodedsignaling using mapping device 106, and builds the encoded transmissionframe including the encoded frame signalling information and the encodedFEC block in frame builder 108. The encoded transmission frames then aretransmitted to receiver 200 through communication channel.

Receiver 200 comprises de-mapping device 202 and FEC decoder 204.Alternatively, like transmitter 100, receiver 200 is also aprocessor-based system and includes one or more processors andassociated memory. In this context, computer programs, or software, arestored in the memory for execution by the processor, e.g., to implementFEC decoder 204. The processor is representative of one or morestored-program control processors and these do not have to be dedicatedto the signalling information process function, e.g., the processor mayalso control other functions of receiver 200. The memory isrepresentative of any storage device, e.g., random-access memory (RAM),read-only memory (ROM), etc.; may be internal and/or external toreceiver 200; and is volatile and/or non-volatile as necessary.

In receiver 200, de-mapping device 202 is adapted to demodulate theencoded signalling information in the received OFDM signal after theencoded frame is split to data symbol and encoded signallinginformation, and FEC decoder 204 is adapted to decode the encodedsignalling information, so that the OFDM frame is recovered based on thedecoded signalling information. In particular, the FEC decoder 204decodes each encoded frame to obtain its signalling parameter, e.g., FFTsize, guard interval pilot pattern choosing, coding rate and modulationscheme. FEC decoder 204 also decodes the encoded signalling informationin the encoded FEC block of the frame, by RM decoding, to obtain FECblock signalling parameters such as code rate and modulation, so thateach FEC data block of the data symbols can be recovered based on thecorresponding FEC block signalling parameters.

Referring now to FIG. 4, a schematic diagram of an encoding scheme forthe transmission frame according to the embodiment is shown. In FIG. 4,the transmission frame includes a preamble for OFDM signalling and datasymbols. As mentioned above, a concatenated code (BCH+S2-LDPC) is usedto protect the OFDM signalling to form an encoded frame signalling.Alternatively, in order to decrease the overhead, the BCH codes can befurther shortened and S2-LDPC can be further punctured based on the OFDMsignaling information bits number requirement in the channelenvironment. Another embodiment is to use the shortened BCH(7032,7200),and punctured DVB-S2 LDPC, which has a code rate of 1/2.

In addition, in FIG. 4, in order to protect FEC block signalinginformation, a Reed-Muller (RM) code is used to encode signallinginformation for each FEC data block, to form an encoded FEC blockincluding FEC data block and encoded FEC block signalling information.The Reed-Muller code can support the majority logic decoder, so itrequires a very short decoding time, which can speed up signalinginformation decoding process at the receiver. In addition, Reed-Mullercodes also have excellent error-performance, which can help to protectthe related signaling information.

In addition, the symmetry structure of RM codewords can help todistinguish this RM codewords from the data stream, so that the FECblock header can be detected easily in the receiver. For example, whenRM code (32, 16) as shown in FIG. 3 is used to encode the FEC blocksignalling information, a RM codewords is obtained by a linearcombination of a 16 rows of the RM generator matrix based on the FECblock signalling information. There exist 6 rows with symmetricstructure in the generator matrix.

In the receiver, when the RM codewords are received, the RMautocorrelation result of the 6 rows with symmetric structure can beused to detect the FEC block header. For example, when the peak value ofthe autocorrelation reaches a predetermined threshold, the startingposition of the autocorrelation is the starting position of the FECblock, that is, the FEC block header.

In another embodiment, a LDPC codes can also be used to encode thesignalling information for each FEC data block. In order to use the LDPCcodes flexibly, a short LDPC code obtained by shorten technique can bedefined in finite geometry and can support multi-step majority logicdecoding, such as (31, 16), (63, 22), (63,37), (255, 21), 255, 175).According to the above embodiment with a FEC block signallinginformation bits number 16, the LDPC code can be shorten to (42, 16).

In a communication transmission environment, especially in cabletransmission, how to overcome the influence of impulsive noise is animportant issue. Referring now to FIG. 5, a schematic diagram of anotherFEC encoding scheme is shown according to another embodiment to overcomeimpulsive noise.

In the embodiment as shown in FIG. 5, the first encoded FEC blockcarries two RM codes, one is the encoded FEC block signalling for thefirst FEC data block, and other is the encoded FEC block signalling ofthe second FEC data block. Accordingly, the L-1th encoded FEC blockcarries the encoded FEC block signalling for both the L-1th FEC datablock and the Lth FEC data block. For the final encoded FEC block of anOFDM frame, it carries the encoded FEC block signalling for both the LthFEC data block and the L-1th FEC data block.

In the embodiment, a specific arrangement of the FEC block encodingscheme is described to implement a repetition signalling protection.However, other repetition signalling protection methods can also beused. For example, one RM module can include more than two RM codes, andif one RM code is be used for Lth FEC block signalling, the other can beused for the L+2th FEC block signalling or another selection based onrequirements of the communication environment. In addition, other codescan also be used to encoding the signalling information of the FEC datablock according to the requirement, so the RM code and LDPC code is justan embodiment of the invention, but not a limitation. According to theembodiment, the two RM codewords can be used to detect the FEC blockheader accurately because of two peak values are occurred in theautocorrelation result.

Although illustrated in the context of separate functional elements,some functional elements previously described may be embodied in one, ormore, integrated circuits (ICs). Similarly, although shown as separateelements, any or all of the elements (e.g., of FIG. 1) may beimplemented in a stored-program-controlled processor, e.g., a digitalsignal processor, which executes associated software. Further, althoughillustrated in the context of a DVB system, the principles of theinvention are applicable to other types of communications systems, e.g.,satellite, Wireless-Fidelity (Wi-Fi), cellular, etc. Indeed, theinventive concept is also applicable to stationary or mobiletransmitters and receivers.

Therefore, the foregoing merely illustrates the embodiment of theinvention and it will thus be appreciated that those skilled in the artwill be able to devise numerous alternative arrangements which, althoughnot explicitly described herein, embody the principles of the inventionand are within its spirit and scope.

1. A method for protecting signalling information in a frame to betransmitted to a receiver in a communication system, comprising:encoding frame signalling information of the frame to protect the framesignalling information; and encoding Forward Error Correction FEC blocksignalling information of FEC blocks in the frame by using Reed-Mullercodes to protect the FEC block signaling information.
 2. The methodaccording to claim 1, further comprising transmitting the frame to thereceiver, and wherein the encoded FEC block signalling information isfollowed by FEC block data of the respective FEC blocks.
 3. The methodaccording to claim 1, further comprising transmitting the frame to thereceiver, and wherein a repetition signalling information protection isused for the respective FEC block.
 4. The method according to claim 1,wherein the FEC block signalling information is encoded by RM codes toform an encoded FEC block signalling information with symmetricstructure.
 5. The method according to claim 1, wherein the framesignalling information is encoded by concatenation codes with innercodes of S2-LDPC codes and outer codes of BCH codes.
 6. A transmitterfor implementing the method for protecting signalling information in aframe to be transmitted to a receiver in a communication system,comprising: means for encoding frame signalling information of the frameto protect the frame signalling information; and means for encodingForward Error Correction FEC block signalling information of FEC blocksin the frame by using Reed-Muller codes to protect the FEC blocksignaling information, said transmitter being preferably adapted toimplementing the method according to claim
 1. 7. A method for receivingsignalling information in a frame from a transmitter in a communicationsystem, comprising: receiving a encoded frame signalling information andencoded FEC block signalling information of the frame; and decoding theencoded signalling information so that a corresponding FEC block data isrecovered, wherein the encoded FEC block signalling information is aReed-Muller codes encoded FEC block signalling information.
 8. Themethod according to claim 7, wherein the decoded FEC block signallinginformation of the corresponding FEC block includes a signallinginformation of another FEC block, and the decoded signalling informationfor the another FEC block is used to recover the another FEC block data.9. The method according to claim 8, wherein the another FEC block is anadjacent FEC block to the corresponding FEC block.
 10. The methodaccording to claim 7, further comprising autocorrelating the RM codesencoded FEC block signalling information to obtain the corresponding FECblock header.
 11. A receiver for receiving signalling information in aframe from a transmitter in a communication system, comprising: meansfor receiving a encoded frame signalling information and encoded FECblock signalling information of the frame; and means for decoding theencoded signalling information to recover the corresponding FEC blockdata, wherein the encoded FEC block signalling information isReed-Muller codes encoded FEC block signalling information, saidreceiver being preferably adapted to implementing the method accordingto claim
 7. 12. A transmitter for implementing the method for protectingsignalling information in a frame to be transmitted to a receiver in acommunication system, said transmitter being preferably adapted toimplementing the method according to claim 1, comprising: FEC encoderfor encoding frame signalling information of the frame to protect theframe signalling information; and encoding Forward Error Correction FECblock signalling information of FEC blocks in the frame by usingReed-Muller codes to protect the FEC block signaling information.
 13. Areceiver for receiving a encoded frame signalling information andencoded FEC block signalling information of a frame from a transmitterin a communication system, said receiver being preferably adapted toimplementing the method according to claim 7, comprising: FEC decoderfor decoding the encoded signalling information to recover thecorresponding FEC block data, wherein the encoded FEC block signallinginformation is Reed-Muller codes encoded FEC block signallinginformation.